Under "construction details" their web site says "we do good" basically and not much more. Might contact forum member 'superduty' with the question. I"m sure he would know. There is really little difference other than the rubber is harder to care for.
* This post was
edited 04/19/12 06:35pm by skipnchar *
2011 F-150 HD Ecoboost 3.5 V6. 2550 payload, 17,100 GCVWR - 2004 F-150 HD (Traded after 80,000 towing miles) 2007 Rockwood 8314SS 34' travel trailer
US Govt survey shows three out of four people make up 75% of the total population