This week I've been working on an antenna that can be used with OpenBeacon2 on multiple bands without the need for an antenna tuner. After a few failed attempts, I settled on an antenna which seems to work well and fit the bill. It is a trap vertical for 40 m, 30 m, 20 m, and 17 m, with elevated quarter wave counterpoises for each band. There's a bifilar 1:1 transformer in the center support of the antenna.
I have been running OpenBeacon 2 on it transmitting WSPR on each of those four bands in succession on random frequencies within the WSPR sub-band. The antenna seems to be working fairly well, as I've been getting spots on all bands (although 17 meters is sparse, I assume because of the lack of sunspots and lack of listeners).
There's a decent chance I'll make PCBs for the band traps and offer them for sale, along with the plans. If you might be interested in testing such an antenna, shoot me an email/message.