I use a Ernst Ultra Stand, it is made of a heavy duty plastic, maybe polyethylene.
It is far stronger than the lightweight foam Robart stand.
My stand has pockets in the base for parts and such, but when I go flying I have lead weights I have made by filling cat food cans or pop cans with melted down scrap lead. (Old wheel balancing weights work great.) I place these weights in the bottom of the stand. My truck has a roll out tray covered with a short nap rug.
With the weights in place the stand will stay in place even during a full power motor test, with a 50" wingspan 3D plane. If I need it while building, I leave the lead weights in the truck. It has a thick foam padding strip that the plane rests on.
For a simple building stand, the foam Robart stand is fine, but I will some times buy a small styrofoam cooler, and cut notches in the edge to fit the plane.
I have seen many different stands from flight boxes that have legs and plane brackets that fold out, to simple X frames as you said.
One of my club members that flys gliders a lot, has custom made wooden trays, narrow but long, fit to his glider fuselages with Velcro straps to hold the plane. On each side of these trays there is a hole drilled in at a slight angle. He has 4" paint rollers with the wire frame but no plastic handles. He inserts the wire where the handle used to be into the holes. the paint rollers are then a soft place for the wing to rest on.
The trays also have a blind nut with the standard threads for a heavy duty tripod, so he can have his glider at any height he wants. And if you loosen the rotation lock, the glider will weather vane and stay pointed into the wind, rather than catching wind under one wing and falling over.