Another thing on the gussets, don't put them in the center of the tube. Put them on the edge. I use my welding magnets across the tube edges, and then stick the gusset against the magnet, then slide it into place next to the tubing. This ensures the gusset is welded to the tangent line of the tubing, not the center. Gussets in the center can actually cut the tubing in case of an accident.
O-O = bad; O_O = good.
Also, gussets should be set to "pull" the joint. A "push" gusset will bend on impact, so it you have a choice of gusset location, make it "pull".
If you are worried about your welding, the important thing is penetration. The best way to ensure good penetration is prep. Make sure your metal is clean, clean, clean. Get every bit of dirt, paint, and rust off it, then spray it with brake cleaner and wipe it down. Wait for the brake cleaner to dry before you strike a spark. Your welds will look better, and more importantly, get better penetration for more strength.
I sandblast, if the part is small enough, or use a flapper wheel, wire brush, or angle grinder. Even a Dremel tool for small areas. Just get it clean.