If I was real concerned I'd do a 'box within a box' for packaging. Bubble wrap the gun, enclose it within a cardboard 'shell' that you can make yourself from a empty box, then bubble wrap over the shell and pack in a suitable box. This type of packing can withstand repeated drops or an atom bomb. Would be cheaper than buying cases too.
Glad to meet another RT user! You got any pics of the old gal?