The latex primer is made for sealing porous surfaces, like wood underlayment. Without it, self-stick tiles may not adhere well, especially to the not exactly uniform chip board surface of the platform. No, I did not paint it first, just painted on the primer. It goes on milk white and dries clear in about an hour. It gives a little tack to the surface. When I tiled the house, I used the primer, then an application of thin-set contact cement (for tiles), then the self-stick tiles. But a floor is exposed and does not have continuous weight. I also had to roll it with a 100 lb. roller. The bed platform will have a constant weight on it, so the extra glue and rolling were not necessary (I hope). If tiles do come loose, I've got glue left over from the house project and can reset them.
In the 3670, the mattress is trapped by the slide walls and the dresser while in transit. Not likely that it will shift around. It still takes a little effort to pull it out of the slide, but it's way easier than it was.
