Complete Waterproof Service Panel AWG 1 Splice
I'd use a Burndy UGSKIT250

For this sort of outdoor/exposed-splice application (as you would find when splicing a triplex or quadruplex overhead feeder or service cable to riser wires in a mast), I would use a Burndy UGSKIT250 for the individual wire splices.  This kit consists of a bare (uninsulated) mechnical splice suitable for 1AWG-250kcmil wire, either copper or aluminum, and a length of heavy wall heat shrink tubing to be shrunk over the top of the splice for waterproofing.  It is UL listed for use outdoors (and even in direct burial applications), and does not require any sort of junction box.