The tourists were ahead within three minutes when awarded a penalty try that led to Namibia hooker Louis van der Westhuizen being sin binned.
Namibia fly-half Tiaan Swanepoel kicked two penalties to reduce the arrears to a single point after 15 minutes at Hage Geingob Stadium, but the home team failed to score again.
As Italy took control, Trullo (twice), inside centre Leonardo Marin, winger Simone Gesi and outside centre Tommaso Menoncello crossed the tryline in the first half.
Fly-half Giacomo Da Re succeeded with four of five conversion kicks to give Italy a 40-6 half-time advantage.
The second half followed a similar pattern with the dominant visitors adding tries through scrum-half Alessandro Fusco, replacements Mirco Spagnolo and Stephen Varney and Trullo.
Italy completed the scoring when awarded another penalty try. Da Ra kicked a further two conversions in the second half and Varney one.
The tourists now head to South Africa to face the world champion Springboks with the first Test on July 5 in Pretoria and the second on July 12 in Gqeberha.