Originally Posted by mk1549
So if you get the thermal windows does this bring the total weight of the 21 to 4600 lbs instead of 4500? Or is the GVWR of 4500 include the possibility of getting them?
GVWR is not the weight of the trailer at all - with or without dual-pane (thermal) windows. It is the Gross Vehicle Weight Rating
, which is the amount which the entire trailer and contents are allowed to weigh. Adding or deleting options or features does not change the GVWR. GVWR depends on the structure and the chassis components (such as the axles and tires); unless those elements are changed, the GVWR does not change.
The base weight of a trailer is the weight without options (about 3050 pounds for an Escape 21'). Since dual-pane windows are optional in any Escape, the base weights do not include them, and so the actual weight of the trailer (what your tug must pull) will be
the base dry weight,
plus the weight of any options or modifications (such as 100 pounds for the extra glass),
plus whatever you have in the tanks (propane, water, and waste),
plus whatever you are carrying in the trailer (your "stuff").
All of that added up is the gross vehicle weight, and it must not exceed the GVWR, which is 4500 pounds for a 21' - whatever type of windows are included. Another way to look at this is that since GVWR is about 1450 pounds more than the base dry weight for a 21', all of your options (such as thermal windows), mods, fluids, and stuff must total no more than 1450 pounds between them (which is typically no problem at all).
Short version of answer:
No, the addition of dual-pane windows does not change the GVWR. Yes, you must still keep the weight of a 21' under 4500 pounds, even if you have dual-pane windows.