Just a quick one.I've got triangular pieces of 3mm steel kindasurrounded in box section if you see what I mean and I wondered if it would be acceptablt to weld a nut to each side of the plate to screw into. Basically its so I can get a little bit of a stand off from the plate on the inside?

Why do you need the stand off?
Could you fit a spacer/turny thing, as in cars seat belts? Otherwise, can't see a problem.

The steel mount that the bolt goes through when bolted down looks like it'll trap the belt that runs through it and instead of welding my plate to the edge of the box section I've welded it along the centre line without thinking so wondered if I could get away with it.

As long as it's not that big, ie 1/2" or less it should be ok. Most harness bolts stand up by at least an inch, so a little bit of extra can't hurt too much.

Aye thats what I thought. Only need a slight bit. Suppose a couple of washers would do but wanted summat a bit more secure

We did the same as you Mr. Grumpy, what I did was put a spacer between the plate and the aluminium, mine isn't welded on and it's a fiddle to put the bolt through but how many times will you need to? I would've welded them on but the chassis was already powdercoated

Cheers Roadkill.SVA'd okay as well I see