Agree about the allowong for possible Flex, mentioned further on up, not Welding up on ALL seams, but at the risk of coming across as a big head further ( as some have taken me ) but having experience growing up on the shop floor in my Dads w/shop-Factory production, General Manufacturing Engineers I was also haunting etc & the being taught ticketed Welding by a Boilermaker later, there's a strong chance, with their high per-hour pay rates, the Fab'ers were also keeping the per bracket weld time to a minimum: as they say time is money ...perhaps do as some mentioned - contact the manufacturer & ask if welds left off to allow for possible avoiding/allowing for flex stress points: but seeing more than a few Australian 'Hadfield' Brand conversions & swap crossmembers etc ( google them) , cross members are usually built for strength/rigidity, so if concerned probably wouldn't hurt to pop a spotweld in the top middle of that square stock & U & maybe 1 ea at ends of plate somewhere to triangulate it up (weld wise) a little & like on hotrod frames fill those exposed gaps with some Bondo/filler to stop dirt collecting ( leave the areas around the welds clear, for stress crack inspection later, if going into a serious transbraked launched, 5,000 stall type E.T. drag car).