Woodstock 1 noted a fair way back in this thread that the P2K's fuselage is the same as, if not similar to, earlier Duralene types, to which almost no
glue will stick ... permanently. To which DocMac in the post above, quite rightly agrees.
However, I have had some success using Contact Cement ... Selley's Quick Grip here in Oz ... which if thinned a little with Automotive Thinners, and left to get tacky before attaching anything (usually wood?) to it, and left to dry out / cure, actually seems to work OK.
I attached a small test strip of 3mm ply, out of the way in a remote area, inside the fuselage, and have had no luck trying to remove it without damaging the actual ply test piece, or worse, possibly damaging the fuselage itself.
Worth considering, I think.
I did successfully use Contact Cement to hold the rear ply part in place in my modified motor mount ... Ref my post, with pictures, a fair way back now, in this thread ... However I also used screws as well, with the glue merely used to hold the part in place.
Hope this may be of some help.