Jim, On the world tex covering you must be talking about your PA-16....I've never used that material and have always covered with super coverite and have never used anything under it to hold, there were a few sags from time to time after sitting but always took them out with a heat gun. I did try balsarite once but didn't like it. However, I did spray my antic fuse and tail surfaces with Lustre Kote clear prior to covering and then brushed on several coats of nitrate after covering and have not had one sag or wrinkle and it's been sitting for over a year waiting for me to finish the wings. Don't know where I came up with that idea but it worked for me and I will be using same when I cover my BUSA cub. I did not sand after spraying...think maybe it stood the wood fibres up and by not sanding there was something there to grab the covering. On the seams....there are several methods and everyone has their own ideas but you can use spackling paste as it accepts paint and can be faired in with light sanding.