The table-toppers burst out the traps to lead 19-0 thanks to two tries and conversions from Lloyd Hayes, plus an Isaac Shaw score.
Matt Jones got Dings on the board before Hayes added to a James Norman effort, only for Crusaders to hit back with George Boulton on target after Sam Cantwell dotted down.
But Travis Gordon grabbed a seven-pointer before the break and Mitchell Lacey-Babalola and Sinjin Broad repeated the trick late on to seal the win for Roth.
Plymouth and Club stay hot on leaders’ heels
Plymouth Albion remain a point back after a 26-20 victory against visitors Tonbridge Juddians.
A Connor Lloyd penalty gave the Kent side an early lead, but the hosts then took control.
Bobby Wigginton, Lucas Gulley, a penalty try and Frankie Dart ensured the bonus-point before the break, Iwan Jenkins with two conversions.
Tom Kendrick replied just before half-time, but second-half scores from Lewis Gjaltema and Curtis Barnes were not enough for TJs.
Third-placed Blackheath cruised to a seventh home win in a row, crushing Birmingham Moseley 55-12.
The away side gained early joy as Freddie Painter went over, only for Club to lead 15-5 at the interval through Raff Hollister, Tom Hughes and Jake Hennessey tries.
The deluge continued with Ed Scragg, Hollister and Billy Harding on the scoresheet, two Sam Morley conversions making it 34-5.
Mose hit back with a penalty try, but seven-pointers from Archie Holland, Kyle McGhie and Hughes took the hosts past their half-century.
Dogs, Park back to winning ways
Sale FC remain fourth after beating bottom side Leicester Lions 52-24 at Heywood Road.
Joe Green converted tries from James Robins and Mark Dixon inside 10 minutes for The Dogs, Theo Mannion getting their opponents on the board.
Green was on target after touching down himself, and made it 28-5 following Corbin Thunder’s try.
Luke Bouchier repeated Green’s trick to cut the deficit to 28-12 at half-time.
Thunder doubled up before Bouchier added to Mannion’s second, only for Thunder to complete his hat-trick.
Jake Metcalfe bagged a bonus for Lions, but Sale had the last word as Robins added to tries from Owen Boxall and Tom Walsh.
Rosslyn Park snapped a two-game losing streak with a 33-19 win at Sedgley Park.
The Londoners built up a 21-0 lead inside 30 minutes as Steffan James converted George Orchard, Sam Kennaugh and Maurice Nwakor scores.
Oli Glasse added to an Adam Mallinson effort to get Tigers on the boar before the break, but Murray Redpath and Benji Marfo ensured Park took five match points home.
Bishop’s Stortford’s trip to Leeds Tykes was postponed due to a frozen pitch.
Rams remain six points off the play-offs after beating Clifton 45-25 at Old Bath Road.
