I've got the opportunity to buy a used Beseler 45 MX enlarger cheaply. It comes with good lenses, but only one negative carrier (4x5). I would need both 135 and 120 neg carriers (at least 6x6 or longer) and don't want to pay more for those than I would the enlarger -- which would be the case if I went through the used department at B&H.
I've been looking at some old threads and have found some references to making my own neg carriers out of mat board. Is this a decent long-term solution? Does the kind of mat board make a difference? Anything else I should consider?