Help installing 1965 Barracuda carpet

I have had trouble in the past trying to keep the cargo area sides from ungluing. So now any time I do a cargo area on a 64-66 I take it to an upholstery shop. I have never had one come unglued when the upholster shop does the cargo area. Its been a few years since I did one but I think they charged me 200 bucks. I did the rest of the carpet