I've disassembled a couple of DTS/RTS sanders by now. I found it not that difficult to do.
You can order the part with the dust port, and indeed, you have to order the 2 metal straps too. The new ones will have a screw on the back to tighten them up.
Take heed though that in order to replace this particular part with the dust port, you have to remove almost every other part and screw you see because it is placed right in the center. Only do this when you are really confident you can put it all back again.