You may just have to overcome your dislike of Peco track. While I am not particularly enraptured about its' appearance, the sleeper base of the 'wooden' sleepered flexible track is a proven product when it comes to resisting degradation caused by UV exposure when laid outdoors. I have Peco code 100 flexible still in use in storage yards, that spent a dozen years as running lines outdoors, until I moved house fourteen years past. There may well be other brands with equivalent or better performance, but others will have to advise on that. I have quite recently seen reports of the rail joiners failing after a few years; that wasn't something I experienced, but that is well in the past.
The points worked reliably, but the base is (or was then) a different polymer formulation from the flexi track base and embrittled over time. The replacements had the sleeper base painted two coats of gloss black before install and there were no problems with them. Try to have as few points as possible outdoors, very vulnerable to windblown and rain splashed dirt in the flangeways and between the open blade and stock rail. Need to check them before every operating session.
As far as I was concerned, life was too short for ballasting the length of run easily achieved outdoors! My solution was a grade of roofing felt with fine mid grey mineralised chippings attached, on top of a timber structure. From the sort of viewing distance typical outdoors, this gave a pleasing apperance, but then I never went for fully scenic anyway. Good to read you are going for timber structure BTW. I am regularly amazed by acccounts of construction of brick, concrete, blockwork, structures which must run tens of kilograms per metre of route, to support a distributed load of a kilo or two per metre maximum. Timber is so much easier to erect, adjust, alter, and finally remove on departure.
