65 x 25 mm steel plate to box section welding?

Although I use metric I had to get my head around the plate dimension. 65 X

25 is like a strip of flat bar one inch thick and two and a half wide. That is an odd piece of material. Your problem is going to be MIG welding 16 gauge to such heavy material. You will have to practice running the bead on the thick material and just washing the edge of the puddle onto the 16 gauge. I would be more inclined to use a 65mm square , 6 mm wall tube instead of the plate material. That plate will be very heavy and lack rigidity. I would not waste time and effort with TIG on such heavy material. Randy

150 amp MIG, I am better with the MIG as the TIG is a new acquisition, which is the better to use? The other snag with the TIG is I only have thin filler rods, and a torch which only takes 3/32 tungstens. Thanks for any advice!

Thanks for the reply, Randy. I think i will weld buttresses into the box section with inserts and bolt the thing together! I'll have a go with my MIG on some off cuts, if it struggles I'll go the bolt together route! I appreciate your concerns, for reasons too long winded for my typing speed i need to use plate side rails.