The Timbren Axle-Less Trailer Suspension System # TASR7KS01 referenced in your question is designed to fit any frame width and can essentially be used as a universal application. This system will work very nicely to replace the axles on your Forest River Fifth Wheel Trailer. As you mentioned, these feature a weight capacity of 7,000 pounds and can provide a little more ground clearance because the 2 independent units can eliminate the need for a thru axle. I do recommend making sure that... view full answer...