I'd like to see photos of the interior of your rig so I can visualize it and understand better how you might install curtain rods/tracks. If, as you say, you want a continuous rod/track the top of the window frames should be aligned horizontally and you'll need places to anchor the rod/track. Anchoring spots could be wood, metal, fiberglass, etc. I, too, am thinking how to do this in my rig, a 13' Scamp
The top of my windows
do not align perfectly, but they are close. I have a fiberglass closet on the left side, fiberglass cabinet above the window in the back and fiberglass side on the right side above the sink. Before I drill any holes I want to be sure the rod/track system would work and would be strong.
I agree with those who said Velcro will not hold well enough. Velcro works well in holding very light
In the close-up photo you can see that I was experimenting with a bottom rod (an old tent pole) attached with a cubicle clip. It did hold well but there is not enough room under the side windows
to do this unless I re-sew ALL my curtains, ugh. I may use a curtain wire (or picture wire) instead on the sides.