I'd be more understanding if Rodimus were an inherently difficult design. He's really not.
Absolutely, or like you said, if this were a novel attempt that isn't just straight
Carve out a sliiiightly bigger space for the car's rear block to fit back into the trailer. Let the spoiler slide forward or something. Maybe have a slide-down piece to complete the pipes. Done. Drop the accessory drawer or the exhaust blast effects if you have to. Just don't let this go into production looking like the two parts don't actually match.
There's a fanmade altmode shell of the front/car half that can plug into the trailer for the full altmode. If not for the cost I'd grab one, as it's not really that much different from what MP09 ended up doing anyway.