Hi! Welcome!... Got pictures?
Vent covers are relatively inexpensive and not too hard to replace. Most of the so called canvas, ain't. It is usually some sort of vinyl on top with the sides being something else. On my Coleman and Viking I used a mild bleach and detergent solution for cleaning the vinyl, sides of the tent I used the mild detergent without the bleach. Bodywork on the camper was the detergent, ditto the top.
is a great place to purchase replacement canvas if you decide the old stuff isn't worth the hassle.
Installing an LP fridge from scratch is not for the faint of heart. You will need to cut holes in the sidewalls to provide for access and ventilation. As well as run LP lines. I have some friends who have an old Viking with the ice box, they use it for storing bread and chips in and drag a dorm sized fridge with them instead. Lot cheaper.