What is the best product to fill in the spaces between the wall board

Caulk

We have a mobile home and where the drywall panels meet there is a space with a strip of molding covering the 'space" We have tried a couple of different ways to solve the issue.

1. Fill the space with a strip of foam board, slightly thinner than the dry wall... then use the dry wall tape and mud to smooth out the wall.... use several thin coats and let dry completely between coats... sand, prime and paint.

2. Bead board Paneling... a better surface for paint than the printed dry wall panels... which have a slightly plastic coating that does not cover well with some paints. Sand the bead board slightly, prime and paint.

3. Wall texture... use a machine that does the same wall texture that they do on ceilings (just lots less rough and bumpy than popcorn) we found that it sticks to the dry wall stuff quite well and that if we used the pre-mixed drywall mud and added a little more water it goes on a little smoother... but it might require 2 thin coats rather than one thick one... sand if needed, prime (2 coats) and paint.

I have also found those gaps are there for a reason. If your house is set on foundation, it probably wouldn't matter as much, If your house is on jacks or pillars there is enough movement to the frame during winds, humidity and temperature changes to pop, or crack a solid seam. Mobile Homes are built to be move-able and remain mobile.

My home was set in place on a sturdy foundation and I too hated the mobile home look of those strips. Removed them all then added some drywall screws here and there where the panels had come loose. Then I just used drywall compound and paper seam tape as with any drywall finishing job. Worked great and was still holding up last time I saw it. There was no problem adhering the compound to the vinyl wrapped board.