Another option is to replace the side windows with "regular" ones that don't utilize a rubber lip seal. I researched this for my (recently sold) U-haul
, and found that the windows Scamp
sells were very likely to be a fit. (IIRC they were exactly the same side-to-side and 1/2" smaller top to bottom. That difference might very well be accounted for by the lip seal; so they might fit just fine as is, or at worst, might require a very small amount of fiberglassing that would subsequently be covered up by the window frame.
A bonus is that you then have the choice of sliding windows, or jalousie windows
(my eternal favorite as I like being able to keep them open rain or shine (or "might rain should I close the window or not; oh wait, I don't have to worry about that").
I priced the same windows from Buccaneer and other companies. and they were going to be around $450 apiece or more; from Scamp
parts department (who must buy in volume), they were about $125 for the sliders and $135 for the jalousie. I think there was about a $20 crating fee, but that would cover two windows if ordered at the same time.
If I had kept the U-haul
, I would have gone that way. Then you can put the windows in with butyl tape, just like everyone else, and also re-seal them when the time comes, with the only "degradable" part being the butyl tape that is easily replaceable - not a rubber seal that is part of the window.
Of course you would want to measure and decide for yourself.
That was my thought, anyway, so I thought I'd post the information.