PLEASE HELP GUINEA PIG HAS HEATSTROKE?

Hi, today its been absolutely boiling and my guinea pigs are in a shed with glass windows, after i came in today he was laying flat on his tummy and had slower breathing, we got him out and offered him lettuce which is his favourite treat, he slowly got up and walked over to it and tried to eat but just slumped onto it, so i looked online and ive got him currently wrapped in a damp clothe in a box with the windows wide open, he is trying to move more as time goes on and he is trying to stand up[ a little bit, but as were in a distant village and all the vets are shut what can i do? Please help thankyou so much i dont want to lose him : (