Help mounting underbody boxes

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So i bought a new truck.  I am taking the body off my old one, and will mount it on the new truck.  I want to mount the underbody toolboxes off the sub frame of the dump as is usually done.  Right now they are mounted to the flatbed, i don't really care for this.In this pic, you can see they use aluminum up front.  Im going to do that.  I need to weld the rear most bracket to the subframe.  What shape steel would you use?  Should i do C channel?  Maybe a large angle?Do they make 3x1.5x .125 steel channel? Attached Images
Reply:Sounds like you don't want the boxes to tilt when the bed dumps, and this is understandable. Yes they make 3" steel channel you speak of, it would be called 3" x 4.1 lb/ft structural channel which is very close to the specs you have listed. I mounted many boxes this way. Easiest thing to do is to take good measurements, cut the channel and paint it, bolt it to the boxes then jack them up to the truck for welding. Otherwise known as the weldon bolton method.Scroll down to the bottom of this list:http://www.engineeringtoolbox.com/am...ls-d_1321.htmlLast edited by polarred21; 10-22-2013 at 09:35 AM.
Reply:You can do that and as said 3"x 4.1lb channel would work good. If the boxes are longer than say 3' mounting to the truck frame on each end causes the boxes to twist more than most can handle and they start to break up, especially the door hinges and latches. For long boxes mounted to the truck frame it's best to use a single tie to the frame and build off that. I use a heavy tube that drops to the bottom of the boxes and welded to a plate that is bolted to the truck frame, then a tube welded across the drop tube to get to the ends of the box. That way when the truck flexes it doesn't twist the box. I had a truck with 2-4' boxes on each side and I had to repair them a bunch of times before the customer finally bit the bullit and had me redo the mounts.
Reply:Brendon, I made mine like a shelf and welded some tabs on the vertical plates so that it meets up with existing holes in the frame from the factory. I also had to add some support to the bottom of my box because it houses the electric dump pump. I also welded diagonal flats for bracing as well. I used whatever I had. It also gives the box a little protection from snow/ice banks when plowing. The pic is the bottom of the mount.www.tjsperformance.comDynasty 300 DXHTP 240HTP Microcut 380Hyperthem 85JD2 Hyd Bender and HF Hyd Ring Roller all in one =(Frankenbender)Bpt. Mill/DRO4' x 8' CNC Plasma TableInstagram: tjsperformanceYT: TJS Welding and Fabrication
Reply:Given a choice, I wouldn't weld to the subframe itself, but bolt it on as they did in the pict you posted..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Thanks for the replies.  Currently yes, i have them mounted very nicely on the bottom of the body.  It doesn't bother me all that much but strikes me as the wrong way to do it.  The boxes just hold soft goods, so its not a super issue.  Hmm, good ideas here.  Will have to mull it over.Tj, i was headed to burr street last friday.  From my memory i believe i passed your place turning right off he highway.Tomorrow i have to finish the body swap, and build a mount for the new filler neck.  Will keep you posted as to what i do.  Getting my new torch tomorrow, excited.
Reply:The mounting with steel channel would be fine but you should use rubber or plastic between the box and the mount. Rubberized undercoat works well also. It doesn't take long for corrosion from electrolis to ruin the box.
Reply:Originally Posted by M J DThe mounting with steel channel would be fine but you should use rubber or plastic between the box and the mount. Rubberized undercoat works well also. It doesn't take long for corrosion from electrolis to ruin the box.
Reply:I usually scrounge up thin rubber and use that.I might just use aluminum channel and weld a bracket on the end.  Then bolt to the sub frame.
Reply:Brendon, I am right across from Ffld Univ.www.tjsperformance.comDynasty 300 DXHTP 240HTP Microcut 380Hyperthem 85JD2 Hyd Bender and HF Hyd Ring Roller all in one =(Frankenbender)Bpt. Mill/DRO4' x 8' CNC Plasma TableInstagram: tjsperformanceYT: TJS Welding and Fabrication
Reply:Thought so, i remember the stone wall.  You welded something on my old toyota years ago.
Reply:Originally Posted by welderjYes I forgot this. This is an important step for aluminum to steel mounting. I use some .050 stainless that I have, but plastic or rubber would work as well. Not sure about the undercoat to, I've seen that rub off and the the electrolysis will quickly eat a hole in the thin panels of the box. Great catch MJD.