If your hitch is "loose" adding weight isn't really a fix, but a band-aid. I suggest that you get a new hitch head welded onto the tongue, just as I had to do with the then 38 y.o. hitch on mine. Also, if you are using a receiver and draw bar hitch, there is a clamp that will stop movement in the receiver and is well worth the investment.
Adding a battery
and an A/C in front will be adding a lot of weight and might offset your tilting problem. If not, just do as I always do and keep the rear stabilizers right inside the back door to be placed as soon as you unhitch.
My reinforcements run parallel to the frame, so as to prevent flexing where the tongue passes under the coach body. Without reinforcing that first I would be careful about adding more weight to the tongue. Keep in mint, that on a good hard bump, that the weight of what's on the tongue can increase 6-8 times dead weight.
As far as danger when welding, not to worry, any experienced welder will know how to protect the bodywork with a heat shield when welding.