What are you doing for your holidays and are your rabbits coming with you? I have known customers buy our collapsable runs and top boxes for housing their bunnies at a UK holiday cottage before. It certainly saves worrying about them while you are away!
Still more of us will have to leave them with a neighbour or friend and try to make the job as easy as possible for our helper. In warm weather the concerns are that shade will be required at all times, plus areas to freely move to when the sun changes position. Use shade wisely, check sun direction and pivot extra shade where needed to make a cool secure spot.
Clay pipes are great for somewhere to take a breath and roof covers are excellent everywhere when its hot but no side ones (to allow good air flow). The pipe may heat up so turfing over sections of it or creating a brick tunnel over it temporarily will cool it down. Burying it will offer the same cooling effect. otherwise shading it with sunshade poised in the right place.
Look out for what happens in the day where the rabbits are kept so you can adjust it to have enough choice of areas while you are away. Ideally allow as access to as many areas as possible so the rabbits choose the best location. Then you need a reliable bunny sitter to be watchful on fresh cold water and offering sprinkled grass or willow - tempting a cooling nibble.
Prepare also for the breaking of the weather, usually a storm. This could create a temporary flood and again covers will protect the rabbit and access to a safe indoor enclosure or off the ground as in a top box or lookout. Anything poised higher could be useful for a short time in heavy rain.
You could have a pile of forage ready for your helper to add to the run and write down your rabbits usual routine as our pets respond better to regularity and repetition. They will hopefully have an enlightening time seeing rabbits through new eyes!