Welding Tips and Tricks

Hey guys I am having a problem bowing tubes as I weld. I am attaching 1/8" plate to 3/16 ga tubing (2x3.5") the tubes are about 10' Long with a 3' span between them just stitch welding it down any ideas how to prevent the bow in the tubing? I am welding about 2" then skipping 22" then coming back and putting one weld 2" between.

Miller Matic 251
17.8V
254 Wire speed
75/25 Gas
.035 Esab solid core wire (er70s6)

Thanks as always guys you are great

Jason,
I think to answer this question best I would need a picture. Some ideas would be to jump around, pre-bend the tube or back stepping the welds. Maybe someone has a good idea though.
-Jonathan