... no hat, wearing only a tank top or t-shirt, and trainers ...
Yeah, cuz that's pretty much like how the Bedouin and other desert peoples dress.
In the era before high-tech outdoor fabrics and garments were common, I found that an oversized white 100% cotton dress shirt from Goodwill and cheap, baggy twill work pants worked for me.
I never actually got around to trying one, but I also thought about a pith helmet (at least when out of sight of others).