Spark Plugs
Recommended are Bosch 4428
Bosch 4308(+2) was replaced by Bosch 4428(+4) which was then discontinued in 2015
Bosch Support line – they confirmed that #4428 was in fact discontinued (in 2015) and the replacement is #8123.(for 1999-2002 Prowlers).
(For 1997 Prowlers their P/N is #6717).
The Autozone Price for Bosch #8123 is $5.29 currently (with a heat range rating of 8). Rockauto has them for $3.59.
The Autozone price for NGK 7781 is $8.19 currently (with a heat range rating of 5). Rockauto has them for $5.00.
The Autozone Price for Champion #7034 is $5.19 (with a heat range rating of 12) Rockauto has them for $3.82
(so go with the brand that you like best)
reference: http://www.sparkplugs.com/learning-center/article/459/discontinued-bosch-spark-plugs
and http://www.boschautoparts.com/en/news/obsolete-superceded-communication