Radio choice for backstage crew

Hi I'm looking for some advice on choice of radios for our backstage crew. We currently use Uniden hand-held units (with mic/earpiece) but we don't get great coverage and the headsets don't last very long (one season is about it). I'm aware that the best solution is a wired communications set but we: a) don't always have the SM, AD, lighting/sound operators in the same place, and b) the SM and ASM need to be free to roam around and remain in contact We're in a large modern hall (about 50m x 25m). Can anyone please offer any alternatives / suggestions etc? Many thanks David