I've used a 12m fiberglass mast up a very big hill for some long weekend stations in the past few years. Was surprisingly stable even in the wind, the whole mast would flex but it wouldn't topple over. Although I did have the telescoping sections collapse in on themselves once overnight, which took the station off air. Seems when rainwater gets in between the sections it lubes up the joints and lets the whole thing telescope down, I suspect once one section goes the others go with it.

Originally it had an end-fed flowerpot using RG58 duct-taped to the side, but I could never get it to match better than 1.5:1 and the coverage was patchy. Later I changed to a ladder line slim jim also taped to the side. That matched easier and gave much better coverage. Running 100W I got good coverage over about 35 miles and furthest reception was 65 miles away up another big hill.

Right now I have a 1/4wave GPA in the loft made from alu tube with the legs just sitting on the floorboards. After some trimming and bending the legs it matches almost perfect to 1.05:1, although moving it at all makes it go out of tune because the alu sheet I used for the centre piece is too thin for the weight of the elements, so the legs flex a lot. I run half a watt into it usually and get full quieting stereo coverage >1 mile away and patchy out to 3-4 miles. Distance record for full quieting was 8 miles with the car radio parked on top of a nearby hill. Also occasionally run 50W and get out to ~20 miles. This is just from the loft of a 2-storey house maybe 10m ASL. I bet it would work great up the really big hill, probably too heavy for the fiberglass mast though.

In a previous property with a decent sized garden, I used a similar mast as a monopole with a #12 wire run up the inside and radials made from alu fence wire buried under the grass. Used on MW with a loading coil wound from #12 wire on a piece of plastic soil pipe, then tuned with an L network using a valve radio tuning cap. Tuned up nice but was very inefficient, only got a couple of miles of staticky coverage with 1W. Probably needed much more power to get anything useful out of it. Also tried winding the loading coil on a ferrite core but found it was too lossy with any ferrite mix that gave a realistic number of turns. It would give a really wideband match which barely changed even with the antenna disconnected, which I figure means all the power was going into the ferrite and not the antenna.

Same antenna worked really well on SW (without the loading coil). Was resonant just above 6.2MHz without any tuning needed. With 5W was picked up on an SDR about 140 miles away.