Onan sells both evap and non.. Evap are made for a rv with a specific / seperate fuel tank.. RV that use the vehicel tank are normally non evap..as here
If it came with the canister kit ,install canister and the purge line that would go to the tank vent/evap line, just make a loop and leave open.. you can get a filter cap if you want
Do not plug it, it vents the carb
I Would NOT try to tee the gen evap into the chassis vent as the factory system may sense a leak and toss a chk eng code..
What happened to your old one,, curious, mike lost spark, i got a unit from a local rv salvage..