If you would go with extruded hard pvc and give 1 to 2 mm room between each sheet, you will be oke.
For example when laying the boards in 25 Celsius temperature 1mm would be enough as a gap, if processing the extruded pvc sheets in 15 Celsius leave a 2 mm gap.
5 Celsius 3 mm gap.
It is perfect hard and resilient stuff, but gets soft in higher temperatures, allow your track for some movement, so dont bolt it down on teh ends.
But more in the middle or at 1/4 of the length from the end.
Keep your sheets at max length of 1.25 meters(standard sheet size is 125 cm by 250cm)
Foam pvc board will stay more ridged and does not have so much of expensive problems.
What i did:
I ordered some materials of 50 x 50 cm, put them into the cooler(+7C) for 4 5 hours, measure it precise at a quarter of a millimetre.
Write it down.
place them into the full sun for 4 to 5 hours, masseur again.
Feel the rigidness of your test boards, incl cutting a 2 inch at the side.
This will help you to determine the material of your choose, plus you will get the feeling on what distance you must place your supporting ribs.
Consider also the following, do you honest think you will leave the track for decades in that spot or is it going to change once in a while.
Could it be more profitable to buy 4 times cheaper osb/chipwood sheet? (redo every 10 years, plus big maintenance?)
Prices in the Netherlands:
osb/chipwood sheet:7 euro per m2
extruded pvc sheet 85 euro per m2
foam sheet: 50 euro per m2
Dont forget you will be needing a caring structure, impregnated wood?(the green soft wood instead of exotic hard woods?)
Aluminium squire pipe seems a perfect mid road/way in between.
Drive some pvc tubes into the ground.
I wanted to make a topic about this, i think this would be a perfect exuse to play in the muddy garden right now
My two cents: make some tests before order a lot of building stuff.
Cheers!