Ted,
They are definitely needed on the 3500# model with the 4” drop. Maybe yours is different.
I don’t know what you have, so, I’m not saying “you did yours wrong”, or “yours will fail!” I actually considered going without a crossbar on mine until I realized the importance of it.
Picture the forces being put on the frame when hitting bumps. Wheels are outside the frame and being pushed up. Nothing is tying those two wheels together, so they will want to separate, or bow out. The bottom frame bows down, and the walls bow in. (If it’s a teardrop).
So you wind up twisting your side side rails of your frame. They take the brunt of the punishment. Everything attached to them takes a little punishment too.
Will you see it at the end of one trip? One season? 2 years? It all depends on how sturdy every other component is. You may get away with it forever.
There are 2x3 pockets on each of the 3500 lb Timbren axles and I believe they recommend 1/4” wall 2x3 square tubing.
Like most, I didn’t want to do it, because it looks like an axle running across, and I bought an “axle-less” suspension! I felt cheated! Well, not really cheated.