Regarding safety concerns: what Big Girtha said.
But also…
It’s sort of hard to describe unless you try it, but I think it’s safe to have a nocturnal erection while doing the BG tuck. When you tuck your entire package back there, the penis can become erect without the shaft being bent. The hard cock simply extends lengthwise in the furrow between your thighs. If you keep your knees bent when you have an erection it’s quite comfortable — your package is essentially aligned under your abdomen like it would be if you were standing up. If you straighten your legs when you have a woody, your package will go back towards your ass and you’ll feel a stretch deep and high in the ligaments that actually feels pretty good.
I was cautious about doing tucks at first because I wasn’t sure if I might be cutting off blood supply. So I spent hours awake in a tuck — like for a whole DVD movie — with no hint of numbness or circulation-cutting constriction. Then I tried falling asleep while tucked, and woke up hours later with my package still back there all fat, dumb and happy.
I urge everyone to be cautious with everything all the time, and test things yourself if you’re at all nervous, but tucks seem safe to me.