Hey Spark,
I did this, so maybe I can offer some insight. I have a GM-90 6/1 and ST-5 and because I'm in hurricane country, needed a way to evacuate it. The concrete base concept is out of the question for me. I went with the frame and trailer option.
I built a frame of heavy walled, steel 2" box beam and bolted two 4x6 treated wooden skids to the bottom of this. The frame holds engine, gennie and radiator, making the unit self-contained. The GM-90 doesn't vibrate much and this frame is more than adequate.
For transportation, I salved a 28' dual axle camper and stripped it down to its bare frame. I cut this down to a toal length of 16', with 12' bed and side rails. Additionally, I heavily gusseted the frame, added a couple of extra cross members and planked the bed with 2x lumber. Overbuilt? Yes, but that's all to the good. It allows me to use the trailer for other jobs and in operation, doesn't really seem to be too much for the listeroid. During a hurricane evacuation, we may travel several hundred miles and it's much more secure to have four tires than two!
As the GM-90 is well balanced, it produces relatively little vibration, but it still does shake to a degree. I chain the rig to the trailer with 3/8ths chain and chain binders front and rear. This allows me to run the machine while it's on the trailer and the vibration is more than tolerable. It should be noted that when it's sitting on the ground and those big skids offer greater ground contact, the vibration is barely noticeable.
It's certainly more noticeanble on the trailer, though, as all vibration is effectively passed to the ground through four tire contact patches.
Based on this experience, if you plan on actually running your engine while on its trailer, I would suggest something heavier than a light, single axle model.
Best regards
Doc