Just make sure where you attach isn't putting all the weight in the middle of the cross bars. Keep the hang point nearer the joins and no problem.
I've got 8 - T-12 4' tubes mounted on a sheet of 1/2 plywood with the ballasts on the back. I recently cut a steel bed frame up to get some thin-wall angle iron to bolt a brace down the back of the plywood cause it was getting so swaybacked that the tubes could easily fall out. Weighs a good 40 pounds. Made that thing 18 years ago and now use it to get the wife's tomatoes going early. She did 50 in solo cups but put them out too early and lost 30 to frost.
The sides fold in on that DIY tent for storage and there is that angle iron running the length of the top on each side to spread the weight from the lights hanging from chains. Didn't trust the 2x2s to hold up over time.
Only had 6 until a couple years ago then finally added the last two. Each pair has a quick connect jack on it's power wire so I can run 2, 4, 6 or all 8 but that's 320W so might as well use a 400w MH by then. Wife likes it tho.