I agree with going for proper BBQ height. I've seen things like that where there were no springs but the axle could be flipped up so the BBQ or whatever could sit at the proper height. Just make sure you put the axle back far enough so you have decent tongue weight. If the axle is too far forward it is very dangerous and the trailer wont track straight at speed. Basically it's like the tail wagging the dog. Off the top of my head, I'd say the axle should be about 3/4 of the way back. If you have a wide spacing for the spring hangers and the axle ends up about in the middle, you'll have to change your design. I had a really old Hobart welder, from the 40's, at one time on a home made trailer with the axle in the middle and I couldn't pull it faster than about 30 MPH or it would start whipping all over the place.
Speaking of Hobart, are you finished and what's your plans for the immediate future?