Personally I don't like tan lines. When using a sunbed there's a certain technique .... Shall we say that you sort of do to make sure you dont have tan lines. But I do go fully nude. Also helps to occasionally move the meat and two veg in case you do happen to get a tan mark on your thigh. That said I see a few blokes above are cincern about burning their cocks, literally never happened to me, and whilst I've only just got into sunbeds again I am the first person to lie out in the garden stark bollock naked to get an all over tan and he's never got burnt, UK based though so kaienofnthat what you will, lol. Also all that being said my partner loves a tan line so recently invested in a thong bathing suit and he seems to like the results.