I used to have three guinea pigs years ago. I was shocked one summers day to discover I'd been offering my guinea pigs warm water.
Although the hutch was partly shaded, the front, which held the water bottle was in sunlight, the sun had heated not only the water, but the metal tip at the end which they drank from, so I had to find a way to shade the water bottle.
For a tunnel for my guinea pigs, mostly for in their run, I had a couple of cut off piece of carpet tube, the thick cardboard tubes that carpets are delivered on; not sure they're classed as safe, but I never had any problems with them.
Guinea pigs are my favourite small pet, we can't afford any more pets at the momnet, but would very much like to keep guinea pigs again, one day.
(Hmmm though not sure how practical that would be with two terrier crosses
)