I have become a firm believer in rotobroach bits. my little 1-1/2 HP drill press struggles with any twist drill above 1" but has no problem drilling a 2" hole through 1 1/2" plate with the rotobroaches.
Using tapered wedges under the edge of a tube is something I have often done to keep the end level while the tube is clamped in a vice I also have several pieces of scrap laying around the drill press that have become dedicated height supports. and don't dare think your are going to clean around it and huck my scrap bits of metal in the bin.