metal tiles behind propane cookstove?

We have a 67 GM bus that has been converted about 20 yrs. ago and needs some updating. We purchesed some metal tiles that have self sticking on the backs, and can take the heat up to 200`F. Now my problem is that the wall behind the propane cookstove, has coated wall paper and down the center is a strip that covers up where the paneling meets. They glued it down good. How do we try to make it where there is no ridge. We have tried wall compound but when the weather got warm it developed a crack down by this strip. We have gotten everything that the tiles indicated. but how do we deal with is problem. Thanks for any of your help.