These youtube videos are for a Boler, but it is identical to the procedure for installing new window gaskets and lockstrip for the Scamp. This is not a job for the faint of heart. 
Glass shops will still install new lockstrip for you and can even cut new plexi or lexan windows. May have to call a few to find one that will do it.
Boler Window Replacement Part 1
Boler Window Replacement Part 2
Lisle 47000 Windshield Locking Strip Tool
Scamp Trailer parts department can send you the lockstrip and gasket for the windows as well as new windows if you need to replace those.
Front and rear window seal: to get the plexiglass into the gasket grove use a cotter pin pulling tool. I use an old craftsman, I bought another brand and had to grind and dull the tip to keep from sticking a hole in the seal. Also lube with Dawn Dish detergent.
Side seals: They shrink with age and end up with gaps on the top and bottom ends, The seals divert the water off the glass from filling the bottom channel. I pull the old seals, I clean and lube and reinstall making sure there is no gap at the bottom and leaving all the gap at the top of the window. Sometimes I seal the ends with black RTV silicone but orig.they were not sealed.
When you compare the new and old side window seals do they look the same? Streching the seal may make the bead small enough to get it to go into the groove.
Eddie
This is a first time install. Previously had original awning style windows. Horribly engineered.
Does the plexi go in the wider gap and the camper shell get sandwiched between the small gap or vice versa? Thanks!