Waterproofing

G'day again folks.
Well tried a small shake down trip with our soft floor camper which hasn't had any use for a couple of years and has been stored outside under 3 layers of silver tarps. Have owned the tent since new and used it many times without a problem.
Well it was a very wet weekend up here and the dome shade tent leaked like a sieve but more importantly the tent had small puddles on the ground side which it has never done before.
Have found that the entire roof gets damp internally about the same as it does when the 2 of us sleep in it on a cold night and the seams let a little through. The inner roof should not have condensation on it to that degree because for 48 hours it has been set up at home with a dehumidifier running in it to ensure the bedding is properly dry unless it's moisture ingress from the seams condensing in there once the dehumidifier was turned off over night so I could have a good look.

What I want to do is re waterproof the roof and all of the seams and looking for some of your experiences with different products. I'm a bit concerned about using unknown products on an onframe tent fearing it might stick the canvas to the frame and not allow it to roll.

Also the dome tent is a parachute material and has been a great asset over the years so not sure if it is worth trying to save or just write it off and fork out the $300 for a new one.

Appriciate any suggestions.