The cracks are typical of high mileage or high rev engines. I've never seen the need to remove the tray, there was a reason Honda choose to rivet it in. One engine I bought had a nasty rattle and it turned out to be a tray that the PO had taken out and then bolted back in.
I also don't think that you will have success with welding unless you are willing to pay a very skilled tig welder. I certainly wouldn't offer any guarantee that there would be even more cracks appearing after welding.
If it was mine and I couldn't find a suitable replacement I would use a silver bearing solder like Stay Brite 8 and Liquid Tec Flux to solder a copper wire over the cracks without removing the tray. You could drill a hole at the end of the crack as well for the soldering but it won't make any difference for welding. Stay brite is far more tolerant of vibrations and far less heat is introduced to the base material compared to welding.