For the water heater (I was doing an Atwood, but same thing would apply to the Suburban) I bought a small roll of #8 mesh (8 squares per inch) stainless steel mesh, commonly used by bee keepers.
I very carefully cut a piece to fit on the inside, as snug as possible, and attached it using .020" stainless aircraft safety wire.
Fridge vent screens are brand specific, if you have a Dometic, you have a Dometic vent and they are sized and shaped different than a Norcold. Dometic has a very rounded end to the vent slots while Norcold is very square with a slightly rounded corner. Most of the screens you buy come with only a few tiny wire ties. For better fit, I again used .020 safety wire, however, I also ordered small black Ty-wraps. Black is weather resistant and won't crack and break like white ones will.
Furnace screens can be found that fit on the inside of the "door" and merely slip into place, though I did wire mine in the corners.
'03 Ram 2500 CTD, 5.9HO six speed std cab long bed Leer top and 2008 Bigfoot 25B21RB.. Previously, 2008 Thor Freedom Spirit 180, SOLD! 2007 Winnebago View 23H Motorhome, SOLD!