Packman followed in the footsteps of Wales star George North, who scored twice in the day’s earlier game against Leinster, as he winged in for a second-half double.
Josh Skelcey, James Wilson, Alex Day and Sam Olver also scored to help Saints secure the victory.
Moseley, like Leinster, provided a good test for the hosts and the Championship team’s power proved hard to live with at times.
But Saints had enough to get the job done, ensuring they remain unbeaten in pre-season ahead of next Friday’s final friendly, at Newport-Gwent Dragons.
Boss Jim Mallinder fielded his internationals in the 33-21 victory against Leinster in the day’s first game, naming a younger team for the clash with Moseley.
And the side from England’s second tier looked sharp early on, earning a penalty that fly-half Caolan Ryan sent wide of the posts.
The men in red didn’t have to wait too long for their first points, though, as wing Michael Penn wrote his name on the scoresheet.
Ryan was more accurate with the boot this time, adding the extras, and the experimental Saints outfit were seven points behind.
But they issued a rapid riposte, with a slick move from left to right resulting in Skelcey dotting down in the corner.
Hooley, who had also started against Leinster, superbly made the kick and he was at it again soon after as Saints scored again.
This time it was Wilson who went over the whitewash as he latched on to a neat pass from scrum-half Day.
While Hooley was showing his class from the tee, Ryan was struggling at the other end, firing another penalty attempt wide.
Moseley were having plenty of the ball though, and after a surge from former Saints centre Scott Armstrong carried them into enemy territory, strong work at the breakdown earned a penalty.
It was used to good effect as another ex-Northampton player, prop Tom Warren, powered his way over to put his team on the cusp of levelling the scores.
Ryan missed the opportunity to restore parity though, failing with a tricky conversion from out wide.
And Saints were soon extending their lead as Day took a quick tap penalty, catching Moseley napping as he dived over to score.
Hooley again added the conversion and Saints moved into the break with a nine-point lead.
Moseley were quick to respond after the interval as their pack turned up the power and replacement hooker Adam Caves made the most of the big push to score.
Ryan struck the conversion well from out wide to cut the gap to two points, but once more it only served to sting Saints into action.
This time it was Packman who went over, showing off his fast feet as he sidestepped his way to the line.
Rory Hutchinson added the extras, but the see-saw nature of the game continued as Moseley’s muscle again told, with Ed Siggery powering over.
Packman got the home fans off their feet soon after, dazzling with a couple more sidesteps as he carried Saints to within a few metres of the line.
And they were soon over again as Olver spotted a gap and showed his strength to hold off a couple of tackles on his way to the line.
Hutchinson again converted and Saints were on their way to second win of the day.
Packman made extra sure, eating up the ground as he crossed the line, with Hutchinson’s conversion rounding off the double success for Saints.
Saints: Wilson (Foster 61); Skelcey, Hutchinson, Hooley (Marshall 50), Packman; Olver, A Day (Robinson 61); E Waller (Parkins 40), Marshall, Denman (Hobbs-Awoyemi 40); Onojaife, Woolford; Conner, Harrison, Dolan (Taylor-Dawes 55).
Moseley: Carter; Cheshire, Armstrong, Owen, Penn; Ryan, Brazier; Warren (Thorp 65), Tolmie (Caves 33), Voisey (Gardiner 50); Powell, Charlton (Dacres 65); Hone, Carpenter (Siggery 33), Mason.