Okay, SouthernCamper, some thoughts for you to ponder. I'm not an expert at this camping stuff so I'm coming at it from the same level you're at probably. ;D Yeah, long post (of course!) - can't help myself.
Regarding darkness - I know some folks have posted they would put something between the shades and the window for heat/cold reflection. You could probably make something with a black fabric backing that would work. You really don't want to start putting velcro on the walls. I already explored that idea when we decided to get cellular shades and nixed that idea quickly. Although you could probably put the adhesive type velcro on the frame of the windows (that wasn't an option for us so not sure if that would work - I'll go look at my windows tomorrow and let you know what I figure out).
Here's a thread I did on the cellular shades we put in our trailer. They were NOT cheap. We did get a bit of a credit from ETI but it certainly didn't cover the cost of the shades. If you go this route, be prepared to spend wads of money. But, with the blackout type shades, they do block a lot of the light (but then again I've not tried it in a super bright WalMart parking lot at night), but some light will come in around the sides.
http://www.escapeforum.org/forums/f8/cellular-shades-are-in-the-trailer-9222.html
You're also going to need to figure something out to cover the light coming in from the door window. As well as the overhead fan. If you want it super dark in there. I've not made any, but have been thinking about it. I was probably going to stick them on with velcro, when I get around to it.
If you're trying to figure out what all it looks like inside, this thread has lots of photos, plus measurements, of the new 21':
http://www.escapeforum.org/forums/f40/lots-of-photos-of-the-new-2017-21-trailer-8286.html
Regarding your son's acid reflux. Been there, dealt with it for years, so I know what it's like. Some thoughts for you on that:
Is he sleeping on more than one pillow? Elevating the head/shoulders helps that crap from coming back up.
I tried that; didn't really work. Also tried elevating the head of the bed; got tired of blanket and sheets sliding down all the time and it didn't really work. Tried the drugs for many years; didn't really work. Wondered if life was worth living like that for the future; obviously I didn't say "no", but it was a close thing at times.
Ended up seeing a nutritionist and in our first meeting she said "well, you know gluten can cause an acidic stomach" and it was like a light went off.
What worked (at first) was getting rid of gluten in my diet. Talk about a bitch to do! Gluten is in lots of stuff.
However, after a while that didn't work, so Dirk did some cruising around on the internet and stumbled across FODMAPs. I won't go into detail other than to say it's even more of a bitch to follow but it's really helped me out a lot, so it's worth it in the end. And it will for anyone with IBS. Let's just say we would not have a trailer if Dirk hadn't discovered FODMAPs (I wasn't seeing the nutritionist by this time, so I don't know if she knew about them as it was rather a new "thing" at the time).
There's several cookbooks I got off Amazon geared for this diet. If you don't tell someone it's gluten free (among other things) they won't think "Oh ick" before even trying what you've made from these recipes.
Read about it on wiki:
https://en.wikipedia.org/wiki/FODMAP
If you really can't travel to see one of the trailers, take the measurements off ETI's site, look at the various photos on this site (the link I gave you, plus many others where folks have posted photos of their trailer, including "2017 and beyond" thread) and then get a measuring tape out and pace out the trailer. Can you guys sleep on the bed/dinette just fine? Is there room to move around the aisle? Enough room in the bathroom? If your son needs a tub bath, that's gonna be a problem.
If you're going to go with a different brand of trailer, you can find oodles of the so-called stick builts at lots of dealers. That's where we started before deciding on a fiberglass trailer. If you're interested in a particular brand, join the forum for that brand. Start reading up on 'em. I was super hot to trot for (ack - blanking on the name now!) a certain small trailer, joined their forum and then started reading about all the problems owners were having. Yeah, crossed that one off my list. Granted, not every single trailer is going to cause problems, but their forums (I joined more than one) really opened my eyes.
R-Pod! Whew, now I won't have to lay awake trying to remember. Yeah, I was really hot for one of them, to put it mildly.
I've only used that sound machine for two nights, but I really like listening to the ocean sounds over the white noise from the machine I've been using for many, many years. I found that if the white noise was too loud, I couldn't relax enough to sleep through it.
Many Escape trailer owners have purchased sight unseen and have been happy with their purchase. Not everyone is able to view any ahead of time. Fortunately, with this forum you can see lots and lots of photos that will help you visualize what they're like. And you can ask lots of questions. Many folks are willing to tromp out to their trailer to take a measurement for you or to snap a photo of whatever you're most concerned about.
Many of the used trailers have sold quickly, but some have sat around for a bit with the price dropping. I don't know if they asked too much to start with (I don't keep track of that, so am clueless about pricing on a used one) or if it's because ETI is/will be producing more trailers and most folks are willing to wait for one they can customize to exactly how they want it.
Laundry - other issue you haven't mentioned. Esp with a toddler, that might be fun. I don't like using commercial washer/dryers after one experience I had while on a long trip. I'm super sensitive to scented stuff and their dryers REEKED of dryer sheets (I can tell when neighbors are drying their clothes - yuck!). The washer didn't get the clothes super dry and I was in a shady spot so it would have taken days to dry the clothes (spring time, not hot summer time). I decided for long trips I'm gonna take this item along. I won't get it until later this year, so I haven't a clue as to how it'll work, but I did a ton of research on various items I could use on the road and this is what I decided to use:
yirego
I know some might laugh over using this, but I feel it'll work for me and it's something for you folks to think about (regarding laundry; not that you need exactly this device).
Good luck!