For purposes of mounting the bracket, straddling a rib doesn't sound like a problem to me. I'd think that having the feeder mounted to the T50's base will give you a more stable base than a rollaround cart would. I suppose if you came up with a way to lock the rollaround cart to the shaper base, effectively securing it so it can't budge, that the cart idea would work just fine. Part of the issue there is the leverage the feeder will put on the cart when the feeder is hanging over the shaper and pushing down on stock.