The original murphy rebel had provisions for a third seat in the cargo area, and several builders have posted pictures of 2 seats (not sure how much fuel they were able to carry in this configuration). In my case, the BRS parachute takes up half the baggage compartment, limiting me to one seat. And the final weight and balance of the aircraft may severely limit how much weight I can realistically place here. Nevertheless, I have to install something if I want to claim 3 seats at inspection.
This is actually a lightweight steel-frame seat used for sporting events (bleacher seats). I wanted steel so I could weld it to a 4130 substructure. That substructure consists of three sections of 1/8" angle stock, and two 2.5" round tube lengths to raise the front of the seat for comfort. The paint was ground down on the seat before welding, and the entire thing was then re-painted black (Image 2).
This flexibility of the whole design hinges on readily available "cargo track" (anodized red was the cheapest). The two lengths of cargo track are attached to 2" channels directly under the floor for reinforcement. Holes for the retaining screws were match-drilled with the cargo track when the floor channels were first installed, greatly facilitating installation. All that remained was to drill out the holes to final size on the cargo-track and install with counter-sunk screws.
The seat structure is attached to 4 quick-release fittings, so the seat can be easily repositioned further aft for more leg room (for shorter individuals), or removed.