RE: TWIN FEVER !!!
A. Spackle (thinned or otherwise - I forget) over/in foam cracked on me one time and showed up eventually under the covering - almost like a wrinkle. Euch, I hate wrinkles (I see enough of them in the mirror).
2. Spackle (I use the lightweight stuff like everyone else) does shrink and I always sand off the first layer and apply a second automatically (no I don't spread it very thick at all - gimme a break).
III. I sealed the edges of FFF with thinned epoxy satisfactorily on last Summer's diesel experiment (still OK). Epoxy seems to be flexible enough to hold up on light structures as well as withstand the rigors of er, unpredicted ground contact.
Four. I have not tried tissue covering over foam. Oh boy a new gimmick to look forward to. (Tissue over laminating film gives a tough old-timey look - alas heavy).
Cinco. I have made a couple of false starts on a project trying to take advantage of the best attributres of balsa and FFF. Youse-all have just stimulated me (oooh, giggle) to keep on truckin'.