50 W radios are not very common. I decided to build an amp to my KX3 to take it with me on shorter tours. The amp is similar to the FT817 Amp Projekt of VK3YY. I made it to operate on 20m, 30m and 40m. Since I use a linked dipole a tuner is not needed. With a 4.5 Ah LiFePo4 Battery I operate up to 2 hours with it.
Searching the net I found something like the MX-P50M which would perhaps be a choice.