These will not be made in anger, but against the savage heat of the sun.
Travelling in a PbP is something I tend to handwave more often than not, but in this case I'm making an exception. This isn't a full blown skill challenge by any means, but it is a possible stumbling block for the party as they make their way across extremely unforgiving terrain.
Technically, wandering monsters don't really exist in 4e, but a distressed party is more likely to attract attention than a particularly able one. We'll see how it goes.