Sprinter 27, I also like the very quiet exhaust of a trials bike. I would really like an electric but their range is too limited for my needs.
I often ride on shared-use trails/areas so quiet and unobtrusive footprint (trials tires/low pressure) are both important elements of considerate sharing and continued access to these areas!
I extend my range with two (1 1/2 gallons each) Primus fuel bottles I carry in my Camelbak, that way, when my bike runs out of fuel, I've got more than enough for the return trip.
I've considered an optional seat but so far, standing is fine.