Rubber questions

I hope I don't get shot for this question.

So as some of you know I just picked up a '67 shell to act as a donor to my running and driving 68 Fish. I'm not certain how long i'll be able to be in this house and I have a garage here, and money is tight. I couldn't pass up this deal as it's the only way that i'll be able to afford to do the body work to my car, due to the fact it needs 2 1/4s 2 front floor pans and a fender. However I just opened Pandora's box and forced my hand.

Once im done with the body work and paint I have to swap over everything off my '68 in case I move I can't afford a storage unit big enough for my household goods that don't fit in an apartment AND 2 cars.

So here's the question...the car is getting blacked out anyway i.e. chrome window strips aren't going back on...do I HAVE to use the windshield gasket or can I use 3m window sealer that is the industry standard for sealing windshields? and will it work for the back window too?