guillows 4500 series

[jlh3rd]

hi
I'm new to this site, and I'll try to get right to the point. I'm building the P40, bonanza, and hellcat 4500 models for the grandkids. I introduced them to the old standard guillows balsa dime store planes and they loved 'em so i'm trying a little upgrade. The problem?, they don't fly very well and i'm just trying to see if there's more i can do,
I've read every post on here about the 4500 series and tips, which i've tried to follow I did use paint pens on them and decals. I guess a no no,but there's that. I rounded all the square edges on the models body and leading edges. I drilled holes in ribs and spar to lighten them. I removed the windows in the bonanza to further lighten it. ....now to balancing
I read and understand the balancing post in here. I've tried to do that,but the one article that everyone likes says to balance without the prop and you can't do that with these, i don't think. Anyway, i use the weights to get to the balance point and then try to adjust the elevator for the best flight characteristics. I've canted the prop slightly to the right for p factor compensation but nothing really seems to help as to consistent flights as i did build one as a test bed without canting the prop and it dove to the left, but now they sometimes dive right AND it depends how much i wind them up.
i can get a good taught covering for the underside of the wing but struggle,as others have said, for the top covering. Is tissue my answer? I figured tissue and kids don't mix. This covering with the kit is pretty tough but is the inconsistent airfoil shape caused by the kit covering causing the unsteady flights? I actually did fairly well with the bonanza on covering ,and reducing weight, but even it wants to fly erratic.
I'm a retired airline pilot so i understand flying and balance but i'm not an aeronautical engineer, so any help is appreciated.
i have pics but says the file is too big.

[jlh3rd]

i've just read that not covering the bottom of the wings on small models can produce more lift, ....comments?