After a slow start by both sides, Tows picked up the pace and rattled over for three quick tries.
The first came from winger Adam Wilkinson who finished off a sweeping move by the Tows backs.
The second was an interception by James Falvey who ran the length of the pitch to score under the posts.
For the third, fly half Ben Roe broke through the midfield to put away full back Matt Yuill. Yuill converted twice.
Tows looked to be in control but a disrupted scrum allowed the hosts back in through a converted try and as the first half finished, Rasen ominously began to lift their game.
Turning round 19-7 up, Tows suffered a terminal setback soon after the restart when they lost No 8 Chris Kirby and skipper Marc Yeates from the back row.
Chrissie George slotted into the back row from the backs, only to be yellow carded shortly afterwards.
With an extra man up front, Rasen brought the score level through two tries from the forwards.
Tows then capitulated, leaking three more tries, allowing the hosts to score 33 unanswered points in the second half.