These types of BAL/Norco frames had issues with flexing and breaking years ago in Kodiak, Aerolite, Jayco, as discussed on this forum. But IIRC that was with trailers longer than 28'. Since then some manufacturers no longer use them (Kodiak) or just use them on trailers 28' or less (Jayco).
We looked at the largest Lance trailer which is about 28' long and has a very wide slide-out. I was concerned that the flexing especially with that big a cut-out in the shell.
But I think the shorter Lance's would be fine. Jayco still uses these frames in their lighter, shorter trailers and I haven't heard of any problems recently.
It's also possible that BAL/Norco has modified their design since the earlier failures, I dunno.